Field of the Invention
The present invention relates to an image processing technique to improve quality of a captured image.
Description of the Related Art
In image capturing by using an image capturing apparatus such as a camera, part of light entering an image capturing optical system may be reflected by a lens surface or a lens holder and may consequently reach an image pickup plane as an unwanted light. The unwanted light that has reached the image pickup plane forms a high-density spot image and broadly covers an object image, thereby becoming ghost or flare. The ghost and the flare each appear as an unwanted component in a captured image.
On the other hand, use of a diffractive optical element with a lens located closest to an object side in a telephoto lens in order to correct axial (longitudinal) chromatic aberration and chromatic aberration of magnification may result in a blurred unwanted light appearing in an entire part of a captured image due to light emitted from a high-luminance object such as the sun existing out of an image-capturing field angle and hitting the diffractive optical element. The unwanted light in this case also appears as the unwanted component in the captured image.
To avoid this problem, methods of optically reducing the unwanted light and methods of removing the unwanted component by digital image processing have been conventionally proposed. As one of the latter methods, Japanese Patent Laid-Open No. 2008-54206 discloses a method of detecting ghost from a difference image indicating a difference between an image (in-focus image) provided through an image capturing optical system is in an in-focus state with respect to an object and another image (defocus image) provided through the image capturing optical system is in an out-of-focus state with respect to the object. In addition, as another one of the latter methods, Japanese Patent Laid-Open No. 2011-205531 discloses a method of comparing multiple viewpoint images provided by three-dimensional image capturing through a single lens and thereby detecting ghost.
However, the method disclosed in Japanese Patent Laid-Open No. 2008-54206 requires the image capturing in the in-focus state and the image capturing in the out-of-focus state, namely, multiple-time image capturing, and thus is not suitable for still image capturing of a moving object and for motion image capturing.
On the other hand, the method disclosed in Japanese Patent Laid-Open No. 2011-205531 can provide multiple parallax images by one-time three-dimensional image capturing through the single lens and thus can be used in the still image capturing of the moving object and in the motion image capturing. However, the method disclosed in Japanese Patent Laid-Open No. 2011-205531 only uses a difference of two images that are a main image and a sub image as the viewpoint images to be compared to detect the ghost, thereby decreasing a ghost detection effect in a case where there are viewpoint images captured from three or more viewpoints.